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Acute Deep Infections of the Upper Extremity: The Utility Of Obtaining Atypical Cultures and Risk Factors for Culture Positivity
Nikolas H Kazmers, MD, MSE;George W Fryhofer, AB; Daniel Gittings, MD; David J. Bozentka, MD; David R. Steinberg, MD; Benjamin L Gray, MD
University of Pennsylvania, Philadelphia, PA

Introduction: Evidence is lacking to guide the decision whether to send atypical cultures (fungal, AFB - acid-fast-bacillus) during surgical debridement of acute deep infections of the upper extremity. The purpose of this study is to elucidate the frequency of positive atypical cultures in this patient population and to determine how these cultures influence the ultimate treatment. Further, we aim to identify factors influencing the yield of atypical cultures.

Materials & Methods: Consecutive adult patients undergoing surgical debridement of acute deep infections of the upper extremity between 2013-2015 were identified retrospectively. Necrotizing infections and superficial infections were excluded. Descriptive statistics were calculated to describe patient baseline characteristics, infection diagnoses, cultures sent during the index surgical procedure with corresponding rates of positivity, and treatments. Clinical records were studied to determine whether management was influenced by positive atypical culture results. Cohorts with positive and negative atypical cultures were compared with univariate analysis for all collected variables (continuous variables - Student t-test or Mann-Whitney, categorical variables - chi-squared or Fisher exact tests). Multivariable logistic regression analysis with a backward stepwise method and the Hosmer-Lemeshow test were performed.

Results: One hundred patients were included (mean age 47.8 years and 7.8 days of preoperative symptoms). Preoperative antibiotics were given to 87%, and 46% of all patients had one or more immunocompromising comorbidities. Diagnoses included soft tissue abscess (46%), suppurative flexor tenosynovitis (22%), septic arthritis (21%), osteomyelitis (9%), and septic bursitis (2%). Aerobic bacterial, anaerobic bacterial, fungal, and AFB cultures were sent in 100%, 99%, 94%, and 82% of patients, respectively. Corresponding rates of positivity were 74%, 34%, 5%, and 2%, respectively (Table 1). Atypical cultures were positive for 7% of patients and 2.9% of all cultures (5/129 fungal, 2/113 AFB). For those with positive atypical cultures, management was influenced for the 3 patients (3% of the cohort) referred for infectious disease consultation and 1 patient (1%) with broadened antimicrobial coverage to include atypical organisms. Univariate analysis demonstrated symptom duration >7 days as potentially associated with atypical culture positivity (OR 6.0 Table 2), which remained as the sole independent predictor in the multivariate model (OR 2.0). Goodness-of-fit testing suggests the multiple regression model satisfactorily fit the data (p=0.06).

Conclusions: In the setting of acute deep infections of the upper extremity, atypical cultures are expensive but infrequently positive (7%) and rarely alter antimicrobial treatment (1%). Symptoms >7 days predict a higher rate of atypical culture positivity.

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